The present invention relates to electrical connection materials and electrical connection methods for electrically connecting a first object electrical connection portion and a second object electrical connection portion.
As an example, portable type information terminals, specifically, electronic equipment such as, for example, portable telephones, are required to be compact and thin, and thus a high density, high resolution circuit employed in such electronic equipment has been developed.
For the connection between an electronic component and a fine electrode, since conventional solder or a rubber connector or the like does not deal with such connection well, an adhesive agent or a film-like material (hereafter, referred to as a connection member) which is anisotropic, excellent in a fine pitch and has conductivity has been employed frequently.
This connection member is comprised of an adhesive agent containing a predetermined amount of conductive material such as conductive particles, and this connection member is provided between a protrusion electrode of an electronic component and a conductive pattern on a printed wiring board and is pressurized conductive pattern on a printed wiring board and is pressurized or pressurized and heated so as to electrically connect both electrodes and to give an insulated relationship to electrodes formed adjacent to the electrodes. Thus, the protrusion electrode of the electronic component and the conductive pattern on the printed wiring board adhere to each other and are fixed.
Basically, as a way to make the connection member described above deal with a fine pitch, by making the particle diameter of the conductive particle smaller than the length of a insulation portion between the adjacent electrodes, the insulated relationship between the adjacent electrodes is ensured, moreover, the content by amount of the conductive particles is set to a value by which the particles do not come into contact with each other, and the particles are made to exist surely on the electrodes to obtain conductivity in the connection portion.
However, in this method, when the diameter of the conductive particle is made small, due to a remarkable increase of the surface area of the conductive particle, the conductive particles cause secondary agglomeration to couple with each other so that the insulated relationship between the adjacent electrodes cannot be maintained.
Further, when the content of the conductive particles is reduced, since the number of the conductive particles on the electrodes to be connected is reduced, the number of contact points becomes insufficient, and conductivity between the connected electrodes cannot be obtained. Thus, it is difficult to make the connection member cope with a fine pitch while maintaining a long period of electrical connection reliability. That is, the finer a pitch conspicuously becomes, the more miniaturization of the electrode area and the space between adjacent electrodes becomes, the conductive particles on the electrodes flow out between the adjacent electrodes together with the adhesive agent due to pressurization or pressurization and heating at the time of connection, thereby preventing realization a fine pitch of the connection member.
In order to solve such problems, conventionally, proposed are a connection member in which the surfaces of conductive particles are coated with an insulation material to increase the number of conductive particles in the connection member and a connection member which is composed of an adhesive layer containing conductive particles and a layer which does not contain conductive particles.
Such conventional connection members are shown in FIG. 10 and FIG. 11.
As shown in FIG. 10, when an object is a glass substrate 200, flatness in a mounting area of an IC (integrated circuit) 201 on the glass substrate 200 is ±0. several μm, and if there is little unevenness (±0. several μm) in heights of protrusion electrodes 202 of the IC 201 as being gold plated bumps, a wiring pattern 203 on the glass substrate 200 and the protrusion electrode 202 of the IC 201 can be electrically connected via conductive particles 205 contained in a connection member 204.
That is, since there is flatness in each component such as an IC, when the thickness of the connection member 204 (generally, approximately 15 to 25 μm, incidentally, an ITO (an oxide of indium and tin) pattern wired on the glass is several Å) is set to the height of the protrusion electrode 202 of the IC 201 plus 5 μm, the connection member 204 is reliably filled along the lower face of the IC 201. Thus, there is no need to make the thickness of the connection member 204 thicker than the thickness needed, and the conductive particles 205 can be sandwiched between the wiring pattern 203 on the glass substrate 200 and the protrusion electrode 202 of the IC 201 at an early stage of a temporary pressurized attachment (pressurization) in the mounting.
Thereafter, even when binder of the connection member 204 flows out at the time of a permanent pressurized attachment (pressurization and heating), the sandwiched conductive particles 205 do not flow, and the wiring pattern 203 on the glass substrate 200 and the protrusion electrode 202 of the IC 201 can be electrically connected reliably via the conductive particles 205 at the time of hardening of the connection member.
FIG. 10(A) shows a state where the connection member 204 (for example, an anisotropic conductive film: ACF) is stuck on the glass substrate 200. The anisotropic conductive film is stuck on the glass substrate 200 generally by performing thermocompression bonding (pressurization and heating: the amount of pressurization is about 100 N/cm2: heating temperature is about 70 to 100° C.). In this state, positioning of the wiring pattern 203 on the glass substrate 200 and the protrusion electrode 202 of the IC 201 is performed.
FIG. 10(B) shows a state where the IC 201 is temporarily attached to the glass substrate 200 by pressure. The temporary pressurized attachment of the IC 201 is performed only by pressurization or pressurization and heating (heating temperature is about 70 to 100° C.).
FIG. 10(C) shows a state where the IC 201 is permanently attached to the glass substrate 200 by pressure. The permanent pressurized attachment of the IC 201 is performed through pressurization and heating, and since the temperature at that time is higher than the glass transition temperature of the anisotropic conductive film, flow of the binder of the connection member 204 occurs. At this time, the conductive particles 205 sandwiched between the protrusion electrode 202 of the IC 201 and the wiring pattern 203 on the glass substrate 200 do not flow, however, the conductive particles 205 other than the sandwiched conductive particles 205 flow to the outside.
FIG. 10(D) shows a state where the anisotropic conductive film is hardened. When the pressurization and heating is performed at the permanent pressurized attachment, resin is hardened after the fluidization thereof. The series of processes are the connection process.
However, when the object is not the glass substrate but is instead a printed wiring board 300 as shown in FIG. 11, and when unevenness in height (± several μm) of wiring patterns 303 occurs or when unevenness in height (±several μm) occurs in such a case where the protrusion electrodes 202 of the IC 201 are gold wire bumps, if the thickness of the connection member 204 corresponds to the height (about 20 μm) of the wiring pattern 303 on the printed wiring board 300 plus the height (about 20 μm) of the protrusion electrode of the IC, it is necessary to further add 10 to 20 μm to the thickness of the connection member 204, considering reliability in the connecting.
In this case, at the early stage of the temporary pressurized attachment (pressurization) of the mounting, since the connection member 204 is thick, the conductive particles 205 cannot be sandwiched between the wiring pattern 303 on the printed wiring board 300 and the protrusion electrode 202 of the IC 201. Thereafter, when the binder of the connection member 204 flows at the time of permanent pressurized attachment (pressurization and heating), the conductive particles 205 also flow similarly, and when the distance between the wiring pattern 303 on the printed wiring board 300 and the protrusion electrode 202 of the IC 201 corresponds to the size of the conductive particle 205, the conductive particles 205 which have flowed are sandwiched during that time. However, the conductive particles 205 do not participate in all connections, and thus electrical connections cannot be obtained. Or since it is necessary to obtain components with strict specifications, the cost increases.
FIG. 11(A) shows a state where the connection member 204 (for example, anisotropic conductive film) is stuck on the printed wiring board 300. The anisotropic conductive film is stuck on the printed wiring board 300 generally by performing thermocompression bonding (pressurization and heating: the amount of pressurization is about 50 to 100 N/cm2: heating temperature is about 50 to 100° C.). In this state, positioning of the wiring pattern 303 on the printed wiring board 300 and the protrusion electrode 202 of the IC 201 is performed.
FIG. 11(B) shows a state where the IC 201 is temporarily attached to the printed wiring board 300 by pressure. The temporary pressurized attachment of the IC 201 is performed only by pressurization or pressurization and heating (heating temperature is about 70 to 100° C.).
FIG. 11(C) shows a state where the IC 201 is permanently attached to the printed wiring board 300 by pressure. The permanent pressurized attachment of the IC 201 is performed through pressurization and heating, and since the temperature at this time is higher than the glass transition temperature of the anisotropic conductive film, flow of the binder occurs. At this time, since there is no conductive particles 205 sandwiched between the protrusion-electrode 202 of the IC 201 and the wiring pattern 303 on the printed wiring board 300, all conductive particles 205 flow as shown by arrows in FIG. 11(C). Thus, when the distance between the wiring pattern 303 on the printed wiring board 300 and the protrusion electrode 202 of the IC 201 corresponds to the size of the conductive particle 205, the conductive particles 205 which have flowed are sandwiched during that time. Therefore, it does not means that the conductive particles 205 exist among all electrodes.
FIG. 11(D) shows a state where the anisotropic conductive film is hardened. When the pressurization and heating is performed at the permanent pressurized attachment, resin is hardened after the fluidization thereof. However, the conductive particles 205 are not sandwiched between the protrusion electrode 202 and the wiring pattern 303, and electrical connection cannot be obtained.
Accordingly, for example, if an electrical connection via conductive particles is obtained reliably regardless of a little unevenness on printed wiring boards to be an object or regardless of a little unevenness of protrusion electrodes of an IC, it is deemed that sufficient reliability is obtained in practical use even on a printed wiring board whose cost is restrained.